If you were using a microphone as the input source it was probably the
sensitivity of the microphone to stray 60hz noise due to an improper shield
termination or the gain turned up too high resulting in picking up the
flourescent lights or positive feedback from the speakers. One way to
combat this effect is to reverse the leads to one of the speakers or both of
them.

If you were using a microphone as the input = source it was=20
probably the sensitivity of the microphone to stray 60hz noise due
to an = improper shield termination or the gain turned up too high =
resulting in=20 picking up the flourescent lights or positive
feedback from the=20 speakers. One way to combat this effect is to
reverse the leads to = one of=20 the speakers or both of them.